The invention includes embodiments that may relate to a heterostructure field effect transistor. The invention includes embodiments that may relate to a method of making and/or using heterostructure field effect transistor.
A field-effect transistor (FET) may be a transistor that relies on an electric field to control the conductivity of a “channel” in a semiconductor material. A FET, like all transistors, may be thought of as a voltage-controlled current source. Some FETs may use a single-crystal semiconductor wafer as the channel, or active region. A terminal in a FET may be one of a gate, a drain, or a source. The voltage applied between gate and source terminals may modulate the current between the source and the drain.
A HFET is a heterostructure field effect transistor, and may be called a HEMT for High Electron Mobility Transistor. A HEET or a HEMT may be a field effect transistor with a junction between two materials with different band gaps (i.e. a heterojunction) as the channel instead of an n-doped region. A conventional combination may include GaAs with AlGaAs. The effect of this junction is to create a thin layer where the Fermi energy may be above the conduction band, giving the channel very low resistance (or to put it another way, “high electron mobility”). This thin layer may be referred to as a two dimensional electron gas. As with other types of FETs, a voltage applied to the gate alters the conductivity of the thin layer.
However, a HFET having such structure is normally-on, that is, the HFET conducts current even in absence of any potential applied between the gate and the source electrode. Therefore, such HFETs are not effective in switching devices, such as inverters or converters.
It may be desirable to have a HFET, which is normally-on and has a low on-resistance. It may be desirable to have a switching device with properties that differ from the properties of available devices.